1. Field of the Invention
This invention relates to a polypropylene composition. More particularly it relates to a high-impact polypropylene composition comprising polypropylene and a chlorinated polyolefin having styrene graft-polymerized thereon (hereinafter abbreviated to Cl.PO-g-St).
2. Description of the Prior Art
Polypropylene is superior in chemical and physical properties and has been used in a large amount as a general-purpose resin, but from a viewpoint of practical physical properties, it has a drawback of being inferior in high-impact strength. In order to overcome this drawback, a great deal of effort and a number of proposals have so far been made, and any of them are roughly classified into a process of blending a rubbery material to polypropylene and a copolymerization process wherein ethylene, butene-1 or the like is used as a copolymerization component in propylene polymerization. The blending process has had drawbacks that if the amount of a rubbery material added is increased in order to increase the high-impact strength of polypropylene, the rigidity and hardness of polypropylene as its merits are notably reduced and further its compatability becomes inferior to reduce its transparency, luster, surface smoothness, etc. On the other hand, the copolymerization process also has had drawbacks that as the amount of copolymerized component is increased, mechanical properties of polypropylene such as rigidity, hardness, etc. become inferior, and also thermal properties such as melting point, softening point, etc. become notably inferior; hence it has been difficult to make these properties consistent with high-impact properties.
The present inventor have made strenuous efforts in order to solve the above-mentioned problems relative to improvement in the high-impact properties of polypropylene, and as a result, have found that when a specified polymer is blended to polypropylene, it is possible to improve the high-impact properties while the reduction in rigidity and hardness is kept minimum.